Ultracold chromium atoms: From Feshbach resonances to a dipolar Bose-Einstein condensate

Year: 2007

Authors: Stuhler J., Griesmaier A., Werner J., Koch T., Fattori M., Pfau T.

Autors Affiliation: Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany

Abstract: We report on experiments with ultracold chromium atoms. Preparing a cloud of 52Cr atoms in a crossed optical dipole trap (CODT) and applying magnetic fields between 4 and 600 G, we observe 14 Feshbach resonances by the occurrence of increased atom loss at distinct magnetic field values. A comparison with theory taking only dipole-dipole coupling into account shows very good agreement between experimental and theoretical resonance positions and allows us to extract the s-wave scattering lengths a6=112(14) a0, a4= 58(6) a0, a2=-7(20) a0 of the involved molecular potentials as well as the dispersion coefficients C6= 733(70) au and

au. The strongest resonance at 589 G has a calculated width of 1.7 G and reveals a three-body loss coefficient below L3, max310-36 m6 s-1. Further evaporative cooling within the CODT leads to the formation of a Bose-Einstein condensate (BEC) with up to 100 000 condensed atoms. The magnetic dipole-dipole interaction between the Cr atoms is so strong that, as a first mechanical manifestation of dipole-dipole interaction, we observe a modification of the condensate expansion which depends on the alignment of the atomic magnetic dipoles with respect to the axis of the CODT. This magnetostrictive effect is in very good agreement with the theory of dipolar quantum gases and shows that a Cr-BEC is an excellent model system to study dipole-dipole interactions in degenerate quantum gases.

Journal/Review: JOURNAL OF MODERN OPTICS

Volume: 54 (5)      Pages from: 647  to: 660

More Information: We thank A. Simoni, E. Tiesinga, P. Pedri, S. Giovanazzi and L. Santos for many fruitful discussions and comments. A. Simoni and E. Tiesinga have performed the assignment of the observed Feshbach resonances and the multichannel scattering calculations to extract the molecular potential parameters. The theory curves regarding the expansion of the dipolar Cr-BEC were calculated by P. Pedri, S. Giovanazzi and L. Santos. This work is funded by the German Science Foundation (DFG) (SPP1116 and SFB/TR 21).
KeyWords: Chromium; Cooling; Magnetic field effects; Molecular polarity; Resonance, Bose Einstein condensate (BEC); Crossed optical dipole trap (CODT); Dipole dipole coupling; Dispersion coefficients; Magnetic dipoles; Molecular potentials, Bose-Einstein condensation
DOI: 10.1080/09500340600677088

Citations: 7
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